Process for forming spirally wound main springs

ABSTRACT

A PROCESS FOR FORMING A SPIRALLY WOUND MAIN SPRING COMPRISES SECURING ONE END OF A STRIP OF SPRING MATERIAL TO A TIMEPIECE COLLET AND THEN ROTATING THE TIMEPIECE COLLET RELATIVE TO THE OTHER END OF THE SPRING STRIP TO SPIRALLY WIND SAME INTO A MAIN SPRING. DURING ROTATION OF THE COLLET, THE WOUND COILS OF THE SPRING ARE RESTRAINED FROM RADIALLY SEPARATING FROM ONE ANOTHER AND AFTER THE SPRING IS FULLY WOUND, THE SPRING IS RELAXED AND THE COILS ARE ALLOWED TO RADIALLY SEPARATE. THE RELAXED SPRING MAY THEN BE SUBJECTED TO A THERMAL TREATMENT TO HEAT-SET THE SPRING.

Dec. 7, 1971 T. BAEHNI 3,624,883

PROCESS FOR FORMING SPIRALLY WOUND MAIN SPRINGS Filed Feb. '7, 1969 F'lG.3c|

INVENTOR: THOMAS BAFIHNT WAJLCEM United States Patent ()1 ice 3,624,883 Patented Dec. 7, 1971 3,624,883 PROCESS FOR FORMING SPIRALLY WOUND MAIN SPRINGS Thomas Baehni, Brugg, Switzerland, assignor to Societe des Fabriques de Spiraux Reunies, Bienne, Switzerland Filed Feb. 7, 1969, Ser. No. 797,456

Claims priority, application Switzerland, Feb. 8, 1968,

1,876/68 Int. Cl. B23p 13/00 US. Cl. 29-177 7 Claims ABSTRACT OF THE DISCLOSURE One of the processes for making hair springs for watches known heretofore consists in securing on the upper part of a broach disposed in the center of a barrel the ends of several spring blades. During winding of the main spring, there is thus obtained several coiled springs, the pitch between each coal being given by the thickness of the intermediate blades. After a thermal treatment, the hair springs are removed from the barrel, separated from one another, after which the inner end of one of the hair springs thus made can, after suitable shaping, be secured and positioned on a collet and such operations are rendered still more complicated by the necessity of flattening and centering the hair spring.

The present invention aims at simplifying these operations and has for its object a process for making a hair spring and fixing the same on a collet which may itself comprise a timepiece balance staff, characterized by the fact that the spring blade is secured on the collet or staff before winding the main spring.

The accompanying drawing shows by way of example certain embodiments of carrying out the process of the invention.

FIG. 1 shows in perspective the collet fixed in the upper part of a broach.

FIGS. 2 and 3 are schematic cross sections of two embodiments.

FIGS. 2a and 3a are top views corresponding to FIGS. 2 and 3.

The device shown in the drawing comprises a broach 1 fast on a rotationally driven shaft 2 and having formed in its upper part a hollow 3 in which is releasably positioned a collet 4. In this example the hollow 3 is a slot with parallel edges but it goes without saying that any other shape, for example a triangular one, would also be possible.

Collet 4 has an opening 5 in which is permanently secured, by simple clamping, welding, gluing or rivetting for example, one end of a length of spring material in the form of a spring blade having a substantially rectangular cross-sectional configuration from which will be formed the hair spring. This collet can be balanced or have any shape whatever. It is also possible to provide a slot .giving elasticity.

The upper end of the broach 1 surrounding collet 4 is rotatably introduced in an opening provided in the center of a tubular member compressing a barrel 6 whose edge has an opening or slit 7 on all its height for the passage therethrough of blade 8 one end of which is secured in the slot 5 of the collet. On the drawing, this slot is radial to the driving broach but it can also be tangent thereto.

In a first embodiment shown in FIGS. 2 and 2a, a cover 9 for the barrel is adjustably mounted on the barrel 6 in such a way as to be in frictional contact with the edge of blade 8 to frictionally brake the natural radial movement of the blade in the direction towards the outer walls of the barrel and to thus obtain the wound blade whose first coil is located against the collet and the upper part of the broach surrounding it and whose succeeding coils touch.

The process of the present invention is carried out by securing one end of the spring blade to the collet by inserting and fastening same in the slot 5. The spring blade is threaded through the opening 7 provided in the tubular barrel and then the collet is rotated relative to the tubular barrel to effect spiral winding of the spring blade into successively overlying coils around the collet. During winding of the spring, the cover member 9 frictionally engages with the coils with sufficient pressure to restrain the coils and prevent them from radially separating and moving outwardly towards side walls of the tubular member 6.

The embodiment shown in FIGS. 3 and 3a comprises additionally a plate 10 having pins 11 positioned in such a way as to form a circle. This plate 10 can slide in the direction of arrow 12 and the pins 11 engage in corresponding openings 13 provided in the bottom of the barrel 6 and eifectively restrain the coils from radially separating and moving radially outwardly towards the side walls of the tubular member 6. During Winding of the main spring, the blade is deformed only in the space existing between the collet-carrying broach and the 'pins. When this space is full, plate 10 is withdrawn and blade 8 relaxes and occupies the volume of the barrel. The assembly is then subjected to a thermal treatment to secure or heat-set the blade in this position.

In a third embodiment, the blade fills the entire free space in the barrel. After winding the main spring, the assembly undergoes a thermal treatment such as when the collet-hair spring assembly is removed from the barrel, the blade relaxes slightly in order to separate the coils.

In the examples given up to now, the central part of the hair spring assumes the shape of the collet. It is naturally possible to form the broach and the collet in such a way as to obtain any curvature at all, for example, a fiat Brguet curve.

In a modification it is also possible to secure the hair spring directly on the balance staff.

What is claimed is:

1. A process for forming a spirally wound main spring secured to a timepiece collet comprising: providing a length of spring material and a timepiece collet; permanently securing one end of said length of spring material to said timepiece collet; and then rotating said timepiece collet relative to the other end of said length of spring material about an axis of rotation to spirally wind said spring material into a main spring.

2. A process according to claim 1; wherein said securing step comprises providing around said timepiece collet and coaxial with said axis of rotation a tubular member having means therein defining a slit, inserting said one end of said spring material through said slit, and then permanently securing said one end to Said timepiece collet; and wherein said rotating step comprises rotating said timepiece collet relative to said tubular member to effect spiral winding of said spring material into successively overlying coils around said timepiece collet.

3. A process according to claim 2; including positively restraining radial separation of said successively overlying coils during said rotating step.

4. A process according to claim 3; wherein said restraining step comprises providing a cover member on said tubular member, and frictionally contacting said cover member with said spring material during spiral winding thereof with sufiicient pressure to prevent radial separation of successively formed coils.

5. A process according to claim 3; wherein said restraining step comprises providing a circular array of pins having a diameter less than that of said tubular member, and inserting said circular array of pins into said tubular member and around said timepiece collet prior to said rotating step to effect spiral winding of Said spring material within the confines of said circular array of pins.

6. A process according to claim 3; further including removing said circular array of pins from said tubular member after the spiral winding of said spring material into a main spring to effect relaxation of the main spring and radial separation of the successively overlying coils; and then thermally treating the relaxed main spring.

7. A process according to claim 2; further including removing said tubular member from around said timepiece collet to effect relaxation of the main spring and radial separation of the successively overlying coils; and then thermally treating the relaxed main spring.

References Cited UNITED STATES PATENTS JOHN F. CAMPBELL, Primary Examiner V. A. DIPALMA, Assistant Examiner U.'S. Cl. X.R. 

